(1) Field of the Invention
The present invention relates to the fabrication of integrated circuit devices, and more particularly, to an advanced process control system using time interval weighting in the fabrication of integrated circuit devices.
(2) Description of the Prior Art
Run by Run (RBR) feedback control schemes have been used widely to control and monitor the semiconductor manufacturing processes. Statistical control is combined with feedback control and uses data from past runs to adjust the recipe for the next run. This method offers the potential for reducing process variability caused by equipment aging, chemical depletion, or fluctuation in ambient conditions with a minimal cost. Integrated device manufacturers use Advanced Process Control (APC) systems to control processing. These types of factories have a very high throughput of a few products. However, there had been no APC theory developed for foundries which make a large number of mixed products, but relatively few of each particular product. A more suitable algorithm must be found for the feed back system for an integrated circuit foundry.
U.S. patent application Ser. Nos. 10/313,501 and 10/749,698 respectively filed on Dec. 6, 2002 and Dec. 31, 2003 teach multivariate run by run process control systems for IC foundries. U.S. Pat. No. 6,304,999 to Toprac et al shows a feedback/feed forward process control system including overlay control. U.S. Pat. No. 6,266,144 to Li teaches a feedback control method for a stepper/scanner. U.S. Pat. No. 6,248,602 to Bode et al discloses a method to store control input parameters such as for overlay control in a photolithography process, process a lot of devices, collect and analyze data for the lot, and perform automated rework based on the data analysis. U.S. Pat. No. 6,245,581 to Bonser et al teaches a method of measuring critical dimension, analyzing the measurement, and performing a secondary etch process based on the analysis. It is desired to find a better way to control feedback data for a foundry situation.